The present invention relates generally to a switch for a light pipe, and more specifically to a device for modulating the intensity of light travelling through a light pipe using ferrofluid to scatter the evanescent field of the light in the light pipe.
In the operation of light pipes it is often desirable to control the intensity of the light propagating in the light pipe. When using high intensity discharge lamps as the light source for light distribution via light pipes, it is desirable to control the light in the light pipe without modulating the light source. Several methods have been used in the past to control the modulation of the light through the light pipe.
A light switch using ferrofluid is described in U.S. Pat. No. 4,384,761. The light pipe is physically separated by a chamber containing ferrofluid. When the coil near the end of the light pipe is energized, the two light pipes cease to be optically coupled. Several problems exist with a system that breaks the continuity of the light pipe. For example, the intensity of propagating light is reduced when the light travels through media with different indices of refraction.
Another light switch is described in commonly owned U.S. patent application Ser. No. 07/980,066 issued on May 3, 1994, U.S. Pat. No. 5,317,667 that uses electrophoresis to control the modulation of light in the pipe without breaking continuity of the light pipe. The present invention seeks further improvements in manufacturability.